Three Possible Ways of Importing VDB Data

The OpenVDB operator does not know about particles and therefore cannot apply VDB grids to particles.

Method 1 - OpenVDB Import, Particle and InitiatorVDB

If you use the "Import" function in OpenVDB then birth a particle and use InitialVDB to let OpenVDB know on which particle to import the grid.

Method 2 - OpenVDB and LoadVDB

Turn off "Import" in OpenVDB

Use LoadVDB to load the .vdb

specify the Target PGroup to generate a particle who will have the VDB data applied

Method 3 - OpenVDB, Particle and LoadVDB

Turn off "Import" in OpenVDB

Birth a particle

Create a LoadVDB and specify the .vdb to load

Connect the "*Born Particle" to the LoadVDB "Particle" input

The particle will now have the .vdb data loaded onto it

Or you turn of the import in the OpenVDB and use instead the LoadVDB, this generate a particle or use the input particle and make the initial and load the grid.